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> Wow! Duple-check and mate and 5 moves. We have yet to have a
> duple-check and mate in an actual game.

Actually I did witness two. By now I had Fairy-Max play many thousands of games, but of course I have been watching only a tiny fraction of that. Perhaps a hundred or so. Both duple-mates occurred in the end-game, though. Typical way for the Persians to finish off a defenseless opponent is to promote two Pawns to Queens, and checkmate with those. If the opponent at that point still has two Kings, duple-mate is sometimes the fastest way.

Two Kings can succesfully defend against a single Queen, btw: KQKK is draw when the Kings protect each other. In this respect the spare King is better than the Rook: in FIDE Chess KQKR is always won.

> Spartan Chess is different armies, of which there are examples only
> 1% or 2% of 4000 CVPage CVs. What about matching Spartan with instead
> of common F.i.d.e. army, the great Betza line-ups, Nutty Knights,
> Colourbound Clobberers, Remarkable Rookies?

This would be interesting, as testing all of the CDA armies would be interesting. With the latest release of WinBoard, I had promoted CDA (in particlar FIDE vs. Clobberers) to the standard choice in the variant that WinBoard knows as 'fairy', and implemented Fairy-Max to play it. (I had to extend Fary-Max' castling code for this, because of the non-standard castling done by the Clobberers, and Adapt WinBoard to allow castling with any corner piece, not just Rooks). Next release of Fairy-Max can switch the variant presented as 'fairy' at run time, and will use this to add some more cases of CDA. (All combinations of Nutty Knights, Color-bound Clobberers and FIDE.)

The Clobberers raise some interesting fundamental questions in the area of piece values, about pair bonuses. The Nutty Knights are not particularly interesting, and to my taste a quite irregular and awkward bunch (too much forwardness, to little retreating capacity). The Remarkable Rookies cannot yet be implemented in Fairy-Max, as it does not support the concept of restricted sliders like the Short Rook. I never looked at the other armies you mention.

IMO Spartan Chess is much more than just another CDA army. The dual Kings give it a very nice twst, and equiping both sides with different Pawn types gives the game a quite different and refreshing 'feel'. Furthermore, the high regularity of its pieces appeals to my sense for symmetry.